Zweischneid I can certainly understand your trepidation, and it was one of the reasons why I had to think hard before bringing in more people into the group. But as time went on and I've seen the methods of roleplaying within the group, I've found that more people are necessary to keep the story going, but also that there really aren't party "roles" per se in a PbP enviroment. Because encounters occur at such a slow pace (because of obviously needing to wait for people to RP before moving forward), the true meat of any character is NOT how well they "do their job" in the traditional tabletop sense, but instead, how interesting and fun is it to write events and conversations for your character. And I've got to say, I get excited every time I see a post for Lynx, because of your details and interesting take on your character. It's just fun to read.
I mean if you think about it, we've been playing for how long and have only had a single combat scenario, which has lasted all of one round. So our combat characters aren't exactly being able to "do their job" either. So with another ranger, and a fighter/rogue, that's two more potential combat characters for a scenario that has thus far not had any combat. LOL. Thus, player enjoyment will come down to party and NPC interaction... making choices for your character, having them do things, and writing reactions to events that occur... none of which is at all tied to your class or "role" in the group. I do not believe you can trule determine your place in a PbP game based on "I'm the only this", or "I'm the only that"... because things move so slowly that who knows if you'll ever even USE those "special abilities" that you yourself only have. If you are a prolific writer and enjoy the interaction, you can be a cleric in a party of eight clerics and still have fun and be a useful part of the party... based entirely on the characterizations you give your character... not how many "unique" abilities you might have.
Anyway, that's my take on things. People might certainly disagree, but if you take a look at how many stats anyone has actually used on their character sheets thus far, I think we'll see just how much crunch really comes into play in a PbP game compared to extemporaneous free writing.